package org.jhlabs.scany.engine.analysis.kr.snowball;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.KeywordAttribute;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.LowerCaseFilter; // javadoc @link

/**
 * A filter that stems words using a Snowball-generated stemmer.
 *
 * Available stemmers are listed in {@link org.tartarus.snowball.ext}.
 * <p><b>NOTE</b>: SnowballFilter expects lowercased text.
 * <ul>
 *  <li>For the Turkish language, see {@link TurkishLowerCaseFilter}.
 *  <li>For other languages, see {@link LowerCaseFilter}.
 * </ul>
 * </p>
 */
public final class SnowballFilter extends TokenFilter {

	private final SnowballProgram stemmer;

	private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);

	private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);

	/**
	 * Construct the english stemming filter.
	 *
	 * Available stemmers are listed in {@link org.tartarus.snowball.ext}.
	 * The name of a stemmer is the part of the class name before "Stemmer",
	 * e.g., the stemmer in {@link org.tartarus.snowball.ext.EnglishStemmer} is named "English".
	 *
	 * @param in the input tokens to stem
	 */
	public SnowballFilter(TokenStream in) {
		super(in);
		try {
			stemmer = new EnglishStemmer();
		} catch(Exception e) {
			throw new RuntimeException(e.toString());
		}
	}
	
	public SnowballFilter(TokenStream input, SnowballProgram stemmer) {
		super(input);
		this.stemmer = stemmer;
	}

	/**
	 * Construct the named stemming filter.
	 *
	 * Available stemmers are listed in {@link org.tartarus.snowball.ext}.
	 * The name of a stemmer is the part of the class name before "Stemmer",
	 * e.g., the stemmer in {@link org.tartarus.snowball.ext.EnglishStemmer} is named "English".
	 *
	 * @param in the input tokens to stem
	 * @param name the name of a stemmer
	 */
	public SnowballFilter(TokenStream in, String name) {
		super(in);
		try {
			Class<?> stemClass = Class.forName("org.tartarus.snowball.ext." + name + "Stemmer");
			stemmer = (SnowballProgram)stemClass.newInstance();
		} catch(Exception e) {
			throw new RuntimeException(e.toString());
		}
	}

	/** Returns the next input Token, after being stemmed */
	@Override
	public final boolean incrementToken() throws IOException {
		if(input.incrementToken()) {
			if(!keywordAttr.isKeyword()) {
				char termBuffer[] = termAtt.buffer();
				final int length = termAtt.length();
				stemmer.setCurrent(termBuffer, length);
				stemmer.stem();
				final char finalTerm[] = stemmer.getCurrentBuffer();
				final int newLength = stemmer.getCurrentBufferLength();
				if(finalTerm != termBuffer)
					termAtt.copyBuffer(finalTerm, 0, newLength);
				else
					termAtt.setLength(newLength);
			}
			return true;
		} else {
			return false;
		}
	}
}
